Bulk conveyors

The basis of all bulk conveyor engineering is the precise definition and accurate classification of materials according to individual characteristics under a specific combination of handling conditions (1). Since the late 1960s there has been an extraordinary growth in research into the fundamental properties and behavior of particulate soHds. However, as of this writing, it is not possible to predict the handling behavior of a bulk soHds material relevant to conditions in a specific conveyor, merely on the basis of the discrete particle properties. 

The bulk soHds conveying industry is interwoven with all aspects of the chemical industry, from mining of raw materials to in-process handling and to final product dehvery. The 1987 value of U.S. product shipments of bulk conveyors and parts was 2.11 biUion according to CEMA. Lists of conveyor manufacturers in the United States (49—51), and worldwide (52) are available. 

Bulk Conveyors for Bulk Materials, DIN 22101 German Standard, 1982. 

The Cohesion Tester has been used in industry, mainly as a quality control-type test. It can be useful as an aid to assessment of flow properties and of power requirements in mixers, bulk conveyors and feeders. The original developers of the tester, Warren Spring Laboratories35, have even tried to correlate the cohesion value with unconfined yield stress determined with the Jenike shear cell and found a good correlation for some powders (fc = 6 x C). The tester is, quite obviously, only useful with fine, cohesive powders because ... 

The eapaeity of these bulk conveyors ean be determined by Equation 9.1 ... 

Nuclear. Mass can be determined directly by measuring changes in the absorption, reflection, or transmission of alpha- or beta-rays, which changes in proportion to the amount of material present. This method is primarily used to determine the mass of bulk material moving on a conveyor. The advantages include the following ... 

Process industries frequently need to weigh and control the flow rate of bulk material for optimum performance of such devices as grinders or pulverizers, or for controlling additives, eg, to water suppHes. A scale can be installed in a belt conveyor, or a short belt feeder can be mounted on a platform scale. Either can be equipped with controls to maintain the feed rate within limits by controlling the operation of the device feeding the material to the conveyor. Direct mass measurement with a nuclear scale can also be used to measure and control such a continuous stream of material. 

Solids. Increasing use of bulk cars, especially of covered hopper cars, has accompanied the expansion of the tank-car fleet. The principal drawback of bulk cars is the requirement for limited use, specialized cars, which necessitates a large investment. However, if such investment can be justified, the cost of transportation for dry bulk materials ia hopper cars usually is less than those for goods ia shipping containers. In many instances, such cars are used in closed-loop service that is, they shuttle in unit trains between filling and discharge points. Similar equipment is also used in specialized highway vehicles whose tmck bodies can incorporate dump hoppers and built-in conveyors. 

The Hquid monomers are suitable for bulk polymerization processes. The reaction can be conducted in a mold (casting, reaction injection mol ding), continuously on a conveyor (block and panel foam production), or in an extmder (thermoplastic polyurethane elastomers and engineering thermoplastics). Also, spraying of the monomers onto the surface of suitable substrates provides insulation barriers or cross-linked coatings. 

Belt Conveyors. A belt conveyor is made up of an endless fabric or elastomer covered belt that traverses between two or more pulleys, and is supported at intermediate points by idler roUs. These conveyors can handle a wide range of materials, from fine powders to large, lumpy stone and coal. Material can be transported at rates of over 5000 t/h and the conveyors operated at belt speeds ranging from 20 to 300 m /min over very long distances. VersatiHty, reHabiHty, and range of capacities have made belt conveyors the most commonly used bulk handling conveyors in industry. 

Other Chain-Type Conveyors. A number of drivea chaia coaveyors are used for coaveyiag bulk soflds ia horizoatal or inclined paths. 

Classification and Definitions of Bulk Materials, CDMA. 550, Conveyor Equipment Manufacturers Association, Rockville, Md., 1988. 

Heat-transfer aspects and performance were studied and reported on by Depew and Farbar (ASME Pap. 62-HT-14, September 1962). Heat-transfer coefficient characteristics are similar to those shown in Sec. 11 for the indirectly heated fluid bed. Another frequent application on plastics is a sm, rather incidental but necessary amount of drying required for plastic pellets and powders on receipt when shipped in bulk to the users. Pneumatic conveyors modifiea for heat transfer can handle this readily. 

Selec tion of the correct conveyor for a specific bulk material in a specific situation is complicated by the large number of interrelated factors that must be considered. First, the alternatives among basic types must be weighed, and then the correc t model and size must be chosen. Workabihty is the first criterion, but the degree of performance perfection that can be afforded must be estabhshed. 

HANDLING OF BULK SOLIDS AND PACKAGING OF SOLIDS AND LIQUIDS TABLE 21-6 Screw-Conveyor Data for 50-lb/fH Material and Pipe-Mounted Sectional Spiral Flights ... 

Since this type of conveyor is available in only one standard size, its capacity is determined by the belt speed and the fixed cross-sectional area. Tons-per-hour capacity is figured by multiplying the bulk density in pounds per cubic foot by the speed in feet per minute and a constant of 0.0021. Power requirements are quite low and figured in the same way as those for conventional belt conveyors. 

Conveyor installations maybe permanent or a combination of permanent and portable. The latter kind is often mounted on a bulk-deliveiy vehicle, which permits fast unloading into the customers silo by the carrier without effort or equipment from the customer. Controls range from simple motor starters and hand-connected hoses to sophisticated, microprocessor-elec tropueumatic control systems. 

Vacuum systems are typically used when flows do not exceed 6800 kg/h (15,000 Ib/h), the equivalent conveyor length is less than 305 m (1000 ft), and several points are to be supplied from one source. They are widely used for finely divided materi s. Of special interest are vacuum systems designed for flows under 7.6 kg/min (1000 Ib/h), used to transfer materials short distances from storage bins or bulk containers to process units. This type of conveyor is widely used in plastics and other processing operations where the variety of conditions requires flexibility in choosing pickup devices, power sources, and receivers. Capital investment can be kept low, often in the range of 2000 to 7000. 

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